1. Field of the Invention
The invention relates to a data transmission arrangement comprising at least a supply voltage source, a transmitter, a receiver and a two-wire data transmission path operated in the differential mode and terminated by its characteristic impedance.
2. Description of the Related Art
Data transmission arrangements are known. They generally serve to transmit digital data, for example within an electronic data processing system. A transmitter supplies the signal to be transmitted to a data transmission path, which is in turn connected to a receiver.
In a very simple version, the transmission path may consist of only one transmission wire and the receiver may consist of a comparator with a fixed reference level, for example at its positive input. The transmission wire is connected in the receiver to the negative input of the comparator. Such a data transmission arrangement is jeopardized, however, by inductive couplings and can be protected therefrom only by a complicated screening. In the case of differences of the supply voltages in the transmitter and in the receiver, problems also occur.
Therefore, more complicated transmission arrangements have two transmission wires and evaluate the voltage difference thereof through a comparator in the receiver. However, these arrangements have the disadvantage that they supply a reception signal only when both transmission wires are coupled. This means that a reception signal can no longer be obtained in the case of disturbance, for example, due to the rupture of a transmission wire. In order to avoid this disadvantage, it is known to provide two additional blocking capacitors. As a result, the reference potentials are separated and only alternating voltage signals, rather than any arbitrary signals, can be transmitted because of the frequency coupling. For this reason, in such arrangements the admissible duration of the same bit state is determined by the duration of charge or discharge of the capacitors, as a result of which only certain data transmission protocols are usable. Although this arrangement already guarantees an automatic level adjustment in the case of a disturbance of a transmission wire, its disadvantages are predominant, however.
A further arrangement is known, in which no capacitors, but analogous blocking switches are used. In this arrangement, an automatic level adjustment in the case of disturbance of a transmission wire is not possible. Therefore, the switches are switched by means of a data processing system and of a corresponding check program. This technique delays the data transmission and moreover provides a complicated design of the data transmission arrangement.
The known arrangements therefore either do not permit a single wire operation or are limited to applications with given data transmission protocols, or cause great delay upon, disturbance such as loss of connection of a transmission wire.